Strictly speaking, petitio principii is not a fallacy of reasoning but an ineptitude in argumentation: thus the argument from p as a premise to p as conclusion

Strictly speaking, petitio principii is not a fallacy of reasoning but an ineptitude in argumentation: thus the argument from p as a premise to p as conclusion is not deductively invalid but lacks any power of conviction, since no one who questioned the conclusion could concede the premise. (this was a quote from the Britannica)